In conventional laser printers, developer cartridges accommodating toner are detachably mounted therein. This type of laser printer is provided with new product detecting means for detecting whether the developer cartridge mounted in the laser printer is a new product and for determining the life of the developer cartridge from the point that the new product was detected.
For example, Japanese Patent Application Publication No. 2000-221781 proposes a developing device in which is provided a sector gear having a recessed part and a protruding part. When a new developing device is mounted in the body of an electrophotographic image forming apparatus, the protruding part formed on the sector gear is inserted into a new product side sensor, turning the new product side sensor on. After the developing device has been mounted in the body of the image forming apparatus, an idler gear is driven to rotate. When the idler gear begins to rotate, the sector gear also rotates, moving the protruding part from the new product side sensor to an old product side sensor. The protruding part is inserted into the old product side sensor, turning the old product side sensor on. At the same time, the idler gear arrives at the recessed part of the sector gear, and the sector gear stops rotating.